Conventionally, hybrid excitation rotating electrical machines including a permanent magnet and an electromagnet are known in the art (see, e.g., Patent Documents 1 and 2). Such a rotating electrical machine includes a rotor and a stator placed radially outward of the rotor to generate a rotating magnetic field rotating the rotor. The stator has a stator core and a stator coil. The rotor has a shaft extending in the axial direction, and first and second cores separated in the axial direction. Each of the first and second cores has permanent magnet excitation magnetic poles that are excited by a permanent magnet, and non-excited permanent magnet non-excitation magnetic poles that are not excited by the permanent magnet, and the permanent magnet excitation magnetic poles and the permanent magnet non-excitation magnetic poles are alternately arranged in the circumferential direction in the radial end of each of the first and second cores. The permanent magnet excitation magnetic poles in the first core and the permanent magnet excitation magnetic poles in the second core have polarities that are inverted with respect to each other. The permanent magnet excitation magnetic poles in the first core are placed so as to face the permanent magnet non-excitation magnetic poles in the second core in the axial direction, and the permanent magnet non-excitation magnetic poles in the first core are placed so as to face the permanent magnet excitation magnetic poles in the second core in the axial direction.
The amount of magnetic flux of the permanent magnet is substantially constant. The rotating electrical machine further includes an exciting coil that excites the permanent magnet non-excitation magnetic poles. When current is applied from the outside to the exciting coil, the exciting coil excites the permanent magnet non-excitation magnetic poles to generate magnetic flux that weakens or strengthen the magnetic flux generated by the permanent magnet. Thus, according to the above rotating electrical machine, the rotor can be appropriately rotated by combined magnetic flux of the magnetic flux of the permanent magnet and the magnetic flux of the electromagnet.